The present invention relates to a printed circuit board boring machine, and more particularly to a machine for boring printed circuit boards by using a drill.
In general, a printed circuit board boring machine is constructed as shown in FIG. 18, which comprises a bed 1 and a table 2 slidably supported on the bed 17 and driven by a drive apparatus (not shown). Drills 3 are prepared in holders 4 fixed to the table 2. A column 5 is provided on the bed 1 so as to straddle the table 2. A spindle carriage 6 is slidably supported to the column 5 and is driven by an action of a Y-axis drive motor 7. A spindle saddle 8 is slidably supported on the spindle carriage 6 and is driven by an action of a Z-axis drive motor 9. Each spindle 10 (FIG. 19) is supported on the spindle saddle 8 and is drivingly rotated by an action of an associated motor 11. A pressure foot 12 is mounted on a cylinder block 13. Reference character W denotes printed circuit boards (hereinafter referred to as boards). The boards W are mounted on the table 2 by standard pins P. The table 2 and the spindle carriage 6 are moved in X- and Y-directions, to thereby locate the printed circuit boards W and the spindles 10 in place. Thereafter, the spindles 10 are moved in the Z-direction to thereby perform the boring work with the drill 3 held at the associated spindles 10.
FIG. 19 shows a structure of the boring portion including a pressure foot 12'.
A spindle 10 and air cylinders 22 are accommodated in the spindle saddle 8. The pressure foot 12' is arranged at the tip ends of the air cylinder 22. With such an arrangement, the printed circuit boards W are located in place by the spindle carriage 6 and the table 2. Thereafter, the spindle saddle 8 is lowered so that the pressure foot 12' depresses a contact plate 17. Then, the spindle 10 is advanced to thereby perform the boring work on the printed circuit boards W. The contact plate 17 is laid on the uppermost board W, and a bottom plate 16 is laid under the lowermost board W. The bottom plate 16 is used for the purpose of preventing the drill 40 from boring the table 2. The contact plate 17 is used for the purposes of enhancing the initial fitting operation of the drill 40 and preventing burrs from being generated upon the drill removal. In general, the contact plate is made of aluminum with a thickness of 0.15 mm to 0.2 mm.
FIG. 20 shows another structure of the spindle portion of the printed circuit board boring machine. In FIG. 20, numeral 29 denotes a cylinder fixed on the spindle saddle 8. An interior of the cylinder 29 is in fluid communication with a compressed air source through a pipe 32. A bearing 33 is engaged with the cylinder 29 to rotatably support the spindle 10. A chuck 34 is fixed to a lower end of the spindle 10 for holding a drill 3. The pressure foot 12 is fixed to the lower end of a piston 35. A discharge port 38 connected to a vacuum suction is formed on a side wall of the pressure foot 12. Grooves for suction of the air during the boring work are formed at a bottom end portion of the pressure foot 12.
The spindle portion shown in FIG. 19 is structured so that an inner diameter D1 of the board pressing portion 30 of the pressure foot 12' is larger than a maximum outer diameter D2 of a drill 40 as shown in FIG. 19. For this reason, in the case of a small diameter drill 3 is used as shown in FIG. 21, the pressure foot 12' presses the boards W at a remote position by a distance L1 from the boring portion of the drill 3. Thus, the drill is likely to be broken.
When the drills are pulled out from the boards W, undesired burrs are formed on the upper side of the printed circuit boards W, so that the boards W are faulty. In order to prevent the generation of burrs upon the pulling-out of the drill, it is necessary to lay the contact plate on the uppermost board W every time when the boards W are to be replaced. In addition, the contact plate 17 can be used only once and thrown away. This is economically disadvantageous.
In the spindle portion shown in FIG. 20, the compressed air having a predetermined pressure is supplied to the cylinder 29 and the piston 35 is moved downwardly. When the spindle saddle 8 shown in FIG. 18 is lowered, the pressure foot 12 presses the boards W as shown in FIG. 22. Thereafter the drill 3 is pushed into the printed circuit boards W to perform the boring work. At this time, the air is sucked into the pressure foot 12 through the grooves 39. Then, the air is discharged from the discharge port 38. Cut chips or powders are discharged from the discharge port 38 and the cooling of the drill 3 is effected by the air sucked through the grooves 39. Also, when the drill 3 is pulled out from the boards W, the burrs are generated on the upper side of the printed circuit boards W, so that the boards are faulty. Therefore, also in this printed circuit board boring machine, the contact plate 17 is laid on the uppermost board W, and the boards are depressed through the contact plate 17 by the pressure foot 12' to prevent the lift or vibration of the printed circuit boards during the boring work to ensure the boring quality and to prevent the damage of the drill. The contact plate 17 suffers from an economical problem such that it is necessary to replace the contact plate with a new one whenever the printed circuit boards W are replaced and the previously used one must be scrapped.
In view of the foregoing defects and difficulties inherent in the conventional machines, an object of the invention is to provide a printed circuit board boring machine which may depress the vicinity of the drill bores in the printed circuit boards in a constant manner irrespective of the diameter of the drills without using the contact plate to be laid on the uppermost board during the boring work of the printed circuit boards, and which may perform the boring work of the printed circuit boards without fail and without any burr in the printed circuit boards.